Natural wetlands collect and purify surface water before it reaches the streams and aquifers that provide our drinking water. They also serve as habitats for many birds and animals, and they provided areas for recreation. Wetland soils are saturated, flooded or ponded such that they develop reducing conditions. Reducing soil conditions typically lead to distinctive biological communities adapted to life in an anaerobic environment, and also foster the development of particular biogeochemical processes that mays provide environmental benefits.
Wetlands have three essential requirements: hydric soils, hydrophytic vegetation, and wetland hydrology. By definition, hydric soils are those that are saturated, flooded, or ponded long enough during the growing season to develop anaerobic conditions in the upper part. That is, hydric soils have a water table at or near surface for a time long enough during the growing season to become anaerobic. In saturated soils anaerobic microorganisms use compounds such as nitrate, manganese oxides and/or iron oxides as at electron acceptor instead of oxygen in respiration processes. A byproduct of this microbial activity is the increased mobility of Mn and Fe in the soil solution. The saturated conditions of the hydrology factor, the soil oxygen deficiency of the vegetation factor, and the anaerobic conditions of the soil factor are all related (U.S. Pat. No. 6,766,762).
Documentation of reduced soil conditions is needed or desired for a number of purposes. For example, wetland construction or restoration projects associated with mitigation efforts usually have hydrological performance standards, but there is an increasing demand for standards linked to wetland function such as demonstrating that soil conditions are reducing. There are also numerous applications linked to hydric soil assessment and the Technical Standard (TS) for Hydric Soils. The TS requires a demonstration both that the soil is saturated and reduced (National Technical Committee for Hydric Soils (2000) Technical Note 11: Technical Standards for Hydric Soils). In the evaluation or testing of Field Indicators of Hydric Soils (USDA-NRCS (2006) FIELD INDICATORS OF HYDRIC SOILS IN THE UNITED STATES, Ver 6.0 (G. W. Hurt et al. (Eds.)) USDA, NRCS, Fort Worth, Tex.), the TS must be met. In cases where a soil does not meet a field indicator, the TS can be used to demonstrate that a soil is hydric. In these situations the soil must be shown to be reducing.
The generally accepted approach to demonstrate reducing conditions in soils is either: (1) to measure the redox potential using Pt electrodes and show that data plot in the “reducing” zone in an Eh-pH diagram or (2) to apply α,α dipyridyl to the soil and observe a positive test (pink color) for ferrous iron. Both of these approaches have limitations due to either the need for specialized equipment or the difficulty in obtaining the necessary chemicals. These limitations have led to recent interest in “IRIS” (“Indicator of Reduction In Soil”) tubes as an alternate approach for confirming reducing conditions in soils (U.S. Pat. No. 6,766,762; Jenkinson, B. et al. (2002) “Soil Hydrology on an End Moraine and a Dissected Drill Plain in West-Central Indiana,” Soil Sci. Soc. Am. J. 66:1367-1376 (2002), Jenkinson, B. (2002) “Indicators of Reduction in Soils (IRIS): Visual Method for the Identification of Hydric Soils,” Ph.D. Diss. Purdue Univ. West Lafayette, Ind.; Castenson, K. L. (2004) “Hydromorphology of Piedmont Floodplain Soils,” M.S. Thesis. Univ. of Maryland, College Park; Jenkinson B. J. and Franzmeier. D. P. (2006) “Development and Evaluation of Fe-Coated Tubes That Indicate Reduction in Soils,” Soil Sci. Soc. Am. J. 70:183-191; Castenson, K. L. and Rabenhorst, M. C. (2006) “Indicator of Reduction in Soil (IRIS): Evaluation of a New Approach for Assessing Reduced Conditions in Soil,” Soil Sci. Soc. Am. J. 70:1222-1226, Rabenhorst, M. C. and Castenson, K. L. (2005) “Temperature Effects on Iron Reduction in a Hydric soil,” Soil Sci. 170:734-742 ). The basic concept of this approach is that a synthetic iron oxide paint is applied to PVC tubes (approx. 21 mm dia.) which are then inserted into the soil. Under wetland conditions, actively respiring microorganisms transfer electrons to the thin coating of iron oxides on the tube, causing the iron to become reduced and soluble, leaving portions of the white tube uncoated. The degree to which the tubes become stripped of the iron oxide paint is an indication of the degree to which microorganisms were using the iron oxides as an alternate electron acceptor.
U.S. Pat. No. 6,766,762, and Jenkinson, B. (2002) (“Indicators of Reduction in Soils (IRIS): A Visual Method for the Identification of Hydric Soils,” Ph.D. Diss. Purdue Univ. West Lafayette, Ind.) give considerable attention to the construction of the tubes themselves as well as some discussion of the nature of the employed paint used to prepare the tubes. Relatively little attention, however, has been given to the mineralogical nature of the paint. Incidental observations have revealed that the disclosed paints provide undesirable adhesion and durability, thus limiting the approach of using IRIS Fe oxide paints.
Thus, despite the above-described efforts, a need remains for an IRIS Fe oxide paint having desirable adhesion and durability. The present invention is directed to this and other goals.